\fracdNdY = \fracn0Y0\fracYY0-2.7,\frac{\mathrm{d}N}{\mathrm{d}\Psi} = \frac{n_0}{\Psi_0}\frac{\Psi}{\Psi _0}^{-2.7}, 相似文献
3.
Coronal bright points, first identified as X-ray Bright Points (XBPs), are compact, short-lived and associated with small-scale, opposite polarity magnetic flux features. Previous studies have yielded contradictory results suggesting that XBPs are either primarily a signature of emerging flux in the quiet Sun, or of the disappearance of pre-existing flux. With the goal of improving our understanding of the evolution of the quiet Sun magnetic field, we present results of a study of more recent data on XBPs and small-scale evolving magnetic structures. The coordinated data set consists of X-ray images obtained during rocket flights on 15 August and 11 December, 1987, full-disk magnetograms obtained at the National Solar Observatory - Kitt Peak, and time-lapse magnetograms of multiple fields obtained at Big Bear Solar Observatory. We find that XBPs were more frequently associated with pre-existing magnetic features of opposite polarity which appeared to be cancelling than with emerging or new flux regions. Most young, emerging regions were not associated with XBPs. However, some XBPs were associated with older ephemeral regions, some of which were cancelling with existing network or intranetwork poles. Nearly all of the XBPs corresponded to opposite polarity magnetic features which wereconverging towards each other; some of these had not yet begun cancelling. We suggest that most XBPs form when converging flow brings oppositely directed field lines together, leading to reconnection and heating of the newly-formed loops in the low corona. 相似文献
4.
This study aims to quantify characteristic features of the bipolar flux appearance of solar intranetwork (IN) magnetic elements.
To attack this problem, we use the Narrowband Filter Imager (NFI) magnetograms from the Solar Optical Telescope (SOT) on board Hinode; these data are from quiet and enhanced network areas. Cluster emergence of mixed polarities and IN ephemeral regions (ERs)
are the most conspicuous forms of bipolar flux appearance within the network. Each of the clusters is characterized by a few
well-developed ERs that are partially or fully coaligned in magnetic axis orientation. On average, the sampled IN ERs have
a total maximum unsigned flux of several 1017 Mx, a separation of 3 – 4 arcsec, and a lifetime of 10 – 15 minutes. The smallest IN ERs have a maximum unsigned flux of
several 1016 Mx, separations of less than 1 arcsec, and lifetimes as short as 5 minutes. Most IN ERs exhibit a rotation of their magnetic
axis of more than 10 degrees during flux emergence. Peculiar flux appearance, e.g., bipole shrinkage followed by growth or the reverse, is not unusual. A few examples show repeated shrinkage–growth or growth–shrinkage,
like magnetic floats in the dynamic photosphere. The observed bipolar behavior seems to carry rich information on magnetoconvection
in the subphotospheric layer. 相似文献
5.
An active region loop system was observed in a decaying active region for three hours by TRACE and BBSO in a joint campaign on September 27, 1998. Continuous mass motion was seen in Hα offband filtergrams throughout the three hours, and some UV loops were exhibited transient brightenings. We find that: (1) cool material was flowing along the loops at a speed of at least 20 km s?1. Further, in Hα red and blue wings, we see mass motion along different loops in opposite directions. This is the first report of a counter-streaming pattern of mass motion in an Hα loop system. (2) Transient brightenings of different UV loops at different times were observed at C?iv 1550 Å. These brightened UV loops were located in the same region and at the same altitudes as the Hα loops. The observations show a clear correlation between the transient brightenings of UV loops and mass motion in Hα loops. (3) Both footpoints of the loop system were located in regions of mixed magnetic polarities. Frequent micro-flares at one footpoint of the loops with small-scale brightenings spreading along the loop leg were observed before the brightening and rising of one C?iv loop. Similar to the case of a filament, the continuous mass motion along the loops seems important for maintaining the cool Hα loop system at coronal height. There may be an indication that the mass motion in cool Hα loops and the correlated transient brightening of the active region loops were due to the small-scale chromospheric magnetic reconnection at the footpoint regions of the loop system. 相似文献6.
We outline a method to determine the direction of solar open flux transport that results from the opening of magnetic clouds
(MCs) by interchange reconnection at the Sun based solely on in-situ observations. This method uses established findings about i) the locations and magnetic polarities of emerging MC footpoints, ii) the hemispheric dependence of the helicity of MCs, and iii) the occurrence of interchange reconnection at the Sun being signaled by uni-directional suprathermal electrons inside MCs.
Combining those observational facts in a statistical analysis of MCs during solar cycle 23 (period 1995 – 2007), we show that
the time of disappearance of the northern polar coronal hole (1998 – 1999), permeated by an outward-pointing magnetic field,
is associated with a peak in the number of MCs originating from the northern hemisphere and connected to the Sun by outward-pointing
magnetic field lines. A similar peak is observed in the number of MCs originating from the southern hemisphere and connected
to the Sun by inward-pointing magnetic field lines. This pattern is interpreted as the result of interchange reconnection
occurring between MCs and the open field lines of nearby polar coronal holes. This reconnection process closes down polar
coronal hole open field lines and transports these open field lines equatorward, thus contributing to the global coronal magnetic
field reversal process. These results will be further constrainable with the rising phase of solar cycle 24. 相似文献
7.
L. K. Harra V. Archontis E. Pedram A. W. Hood D. L. Shelton L. van Driel-Gesztelyi 《Solar physics》2012,278(1):47-71
In this paper we analyse the flux emergence that occurred in the following polarity area of an active region on 1 – 2 December
2006. Observations have revealed the existence of fast outflows at the edge of the emerging flux region. We have performed
3-D numerical simulations to study the mechanisms responsible for these flows. The results indicate that these outflows are
reconnection jets or pressure-driven outflows, depending on the relative orientation of the magnetic fields in contact (i.e. the emerging flux and the active region’s field which is favourable for reconnection on the west side and nearly parallel
with the pre-existing field on the east side of the emerging flux). In the observations, the flows are larger on the west
side until late in the flux emergence, when the reverse is true. The simulations show that the flows are faster on the west
side, but do not show the east flows increasing with time. There is an asymmetry in the expansion of the emerging flux region,
which is also seen in the observations. The west side of the emerging flux region expands faster into the corona than the
other side. In the simulations, efficient magnetic reconnection occurs on the west side, with new loops being created containing
strong downflows that are clearly seen in the observations. On the other side, the simulations show strong compression as
the dominant mechanism for the generation of flows. There is evidence of these flows in the observations, but the flows are
stronger than the simulations predict at the later stages. There could be additional small-angle reconnection that adds to
the flows from the compression, as well as reconnection occurring in larger loops that lie across the whole active region. 相似文献
8.
The Recovery of CME-Related Dimmings and the ICME’s Enduring Magnetic Connection to the Sun 总被引:1,自引:1,他引:0
G. D. R. Attrill L. van Driel-Gesztelyi P. Démoulin A. N. Zhukov K. Steed L. K. Harra C. H. Mandrini J. Linker 《Solar physics》2008,252(2):349-372
It is generally accepted that transient coronal holes (TCHs, dimmings) correspond to the magnetic footpoints of CMEs that
remain rooted in the Sun as the CME expands out into the interplanetary space. However, the observation that the average intensity
of the 12 May 1997 dimmings recover to their pre-eruption intensity in SOHO/EIT data within 48 hours, whilst suprathermal
unidirectional electron heat fluxes are observed at 1 AU in the related ICME more than 70 hours after the eruption, leads
us to question why and how the dimmings disappear whilst the magnetic connectivity is maintained. We also examine two other
CME-related dimming events: 13 May 2005 and 6 July 2006. We study the morphology of the dimmings and how they recover. We
find that, far from exhibiting a uniform intensity, dimmings observed in SOHO/EIT data have a deep central core and a more
shallow extended dimming area. The dimmings recover not only by shrinking of their outer boundaries but also by internal brightenings.
We quantitatively demonstrate that the model developed by Fisk and Schwadron (Astrophys. J.
560, 425, 2001) of interchange reconnections between “open” magnetic field and small coronal loops is a strong candidate for the mechanism
facilitating the recovery of the dimmings. This process disperses the concentration of “open” magnetic field (forming the
dimming) out into the surrounding quiet Sun, thus recovering the intensity of the dimmings whilst still maintaining the magnetic
connectivity to the Sun.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
9.
The manifestation of convection in deep layers of the Sun has been found in the dynamics of solar surface activity (Arkhypov,
Antonov, and Khodachenko in Solar Phys.
270, 1, 2011). Some chromospheric phenomena could be connected with deep convection, too. We justify this hypothesis with sunspot, Ca ii, Hα, and millimeter-wave radio data. It is argued that large-scale (20 to 25 deg) bright regions in the chromosphere, surrounded
by dark halos with diameters of 40° to 50°, can be manifestations of giant convection cells. The ascending and descending
flows in such cells modulate the emergence of magnetic tubes generating the high-temperature regions and low-temperature halo
in the chromosphere. Our estimates of the rotation rate of such features confirm their association with deep (≳ 35 Mm) layers
of the solar convection zone. 相似文献
10.
The Extreme ultraviolet Imaging Spectrometer (EIS) onboard Hinode is the first solar telescope to obtain wide-slit spectral images that can be used for detecting Doppler flows in transition
region and coronal lines on the Sun and to relate them to their surrounding small-scale dynamics. We select EIS lines covering
the temperature range 6×104 to 2×106 K that give spectrally pure images of the Sun with the 40-arcsec slit. In these images Doppler shifts are seen as horizontal
brightenings. Inside the image it is difficult to distinguish shifts from horizontal structures but emission beyond the image
edge can be unambiguously identified as a line shift in several lines separated from others on their blue or red side by more
than the width of the spectrometer slit (40 pixels). In the blue wing of He ii, we find a large number of events with properties (size and lifetime) similar to the well-studied explosive events seen in
the ultraviolet spectral range. Comparison with X-Ray Telescope (XRT) images shows many Doppler shift events at the footpoints
of small X-ray loops. The most spectacular event observed showed a strong blue shift in the transition region and lower corona
lines from a small X-ray spot that lasted less than 7 min. The emission appears to be near a cool coronal loop connecting
an X-ray bright point to an adjacent region of quiet Sun. The width of the emission implies a line-of-sight velocity of 220 km s−1. In addition, we show an example of an Fe xv shift with a velocity of about 120 km s−1, coming from what looks like a narrow loop leg connecting a small X-ray brightening to a larger region of X-ray emission. 相似文献
11.
Outflows at the Edges of an Active Region in a Coronal Hole: A Signature of Active Region Expansion?
Outflows of plasma at the edges of active regions surrounded by quiet Sun are now a common observation with the Hinode satellite. While there is observational evidence to suggest that the outflows are originating in the magnetic field surrounding
the active regions, there is no conclusive evidence that reveals how they are driven. Motivated by observations of outflows
at the periphery of a mature active region embedded in a coronal hole, we have used a three-dimensional simulation to emulate
the active region’s development in order to investigate the origin and driver of these outflows. We find that outflows are
accelerated from a site in the coronal hole magnetic field immediately surrounding the active region and are channelled along
the coronal hole field as they rise through the atmosphere. The plasma is accelerated simply as a result of the active region
expanding horizontally as it develops. Many of the characteristics of the outflows generated in the simulation are consistent
with those of observed outflows: velocities up to 45 km s−1, properties akin to the coronal hole, proximity to the active region’s draining loops, expansion with height, and projection
over monopolar photospheric magnetic concentrations. Although the horizontal expansion occurs as a consequence of the active
region’s development in the simulation, expansion is also a general feature of established active regions. Hence, it is entirely
possible and plausible that the expansion acceleration mechanism displayed in the simulation is occurring in active regions
on the Sun and, in addition to reconnection, is driving the outflows observed at their edges. 相似文献
12.
This paper is the second in a series of studies working towards constructing a realistic, evolving, non-potential coronal
model for the solar magnetic carpet. In the present study, the interaction of two magnetic elements is considered. Our objectives
are to study magnetic energy build-up, storage and dissipation as a result of emergence, cancellation, and flyby of these
magnetic elements. In the future these interactions will be the basic building blocks of more complicated simulations involving
hundreds of elements. Each interaction is simulated in the presence of an overlying uniform magnetic field, which lies at
various orientations with respect to the evolving magnetic elements. For these three small-scale interactions, the free energy
stored in the field at the end of the simulation ranges from 0.2 – 2.1×1026 ergs, whilst the total energy dissipated ranges from 1.3 – 6.3×1026 ergs. For all cases, a stronger overlying field results in higher energy storage and dissipation. For the cancellation and
emergence simulations, motion perpendicular to the overlying field results in the highest values. For the flyby simulations,
motion parallel to the overlying field gives the highest values. In all cases, the free energy built up is sufficient to explain
small-scale phenomena such as X-ray bright points or nanoflares. In addition, if scaled for the correct number of magnetic
elements for the volume considered, the energy continually dissipated provides a significant fraction of the quiet Sun coronal
heating budget. 相似文献
13.
Pankaj Kumar Ablishek K. Srivastava B. Filippov R. Erdélyi Wahab Uddin 《Solar physics》2011,272(2):301-317
We present the multiwavelength observations of a flux rope that was trying to erupt from NOAA AR 11045 and the associated
M-class solar flare on 12 February 2010 using space-based and ground-based observations from TRACE, STEREO, SOHO/MDI, Hinode/XRT, and BBSO. While the flux rope was rising from the active region, an M1.1/2F class flare was triggered near one of its
footpoints. We suggest that the flare triggering was due to the reconnection of a rising flux rope with the surrounding low-lying
magnetic loops. The flux rope reached a projected height of ≈0.15R
⊙ with a speed of ≈90 km s−1 while the soft X-ray flux enhanced gradually during its rise. The flux rope was suppressed by an overlying field, and the
filled plasma moved towards the negative polarity field to the west of its activation site. We found the first observational
evidence of the initial suppression of a flux rope due to a remnant filament visible both at chromospheric and coronal temperatures
that evolved a couple of days earlier at the same location in the active region. SOHO/MDI magnetograms show the emergence
of a bipole ≈12 h prior to the flare initiation. The emerged negative polarity moved towards the flux rope activation site,
and flare triggering near the photospheric polarity inversion line (PIL) took place. The motion of the negative polarity region
towards the PIL helped in the build-up of magnetic energy at the flare and flux rope activation site. This study provides
unique observational evidence of a rising flux rope that failed to erupt due to a remnant filament and overlying magnetic
field, as well as associated triggering of an M-class flare. 相似文献
14.
Coronal holes (CH) emit significantly less at coronal temperatures than quiet-Sun regions (QS), but can hardly be distinguished in most chromospheric and lower transition region lines. A key quantity for the understanding of this phenomenon is the magnetic field. We use data from SOHO/MDI to reconstruct the magnetic field in coronal holes and the quiet Sun with the help of a potential magnetic model. Starting from a regular grid on the solar surface we then trace field lines, which provide the overall geometry of the 3D magnetic field structure. We distinguish between open and closed field lines, with the closed field lines being assumed to represent magnetic loops. We then try to compute some properties of coronal loops. The loops in the coronal holes (CH) are found to be on average flatter than in the QS. High and long closed loops are extremely rare, whereas short and low-lying loops are almost as abundant in coronal holes as in the quiet Sun. When interpreted in the light of loop scaling laws this result suggests an explanation for the relatively strong chromospheric and transition region emission (many low-lying, short loops), but the weak coronal emission (few high and long loops) in coronal holes. In spite of this contrast our calculations also suggest that a significant fraction of the cool emission in CHs comes from the open flux regions. Despite these insights provided by the magnetic field line statistics further work is needed to obtain a definite answer to the question if loop statistics explain the differences between coronal holes and the quiet Sun. 相似文献
15.
We study variations of the lifetimes of high-ℓ solar p modes in the quiet and active Sun with the solar activity cycle. The lifetimes in the degree range ℓ=300 – 600 and ν=2.5 – 4.5 mHz were computed from SOHO/MDI data in an area including active regions and quiet Sun using the time – distance
technique. We applied our analysis to the data in four different phases of solar activity: 1996 (at minimum), 1998 (rising
phase), 2000 (at maximum), and 2003 (declining phase). The results from the area with active regions show that the lifetime
decreases as activity increases. The maximal lifetime variations are between solar minimum in 1996 and maximum in 2000; the
relative variation averaged over all ℓ values and frequencies is a decrease of about 13%. The lifetime reductions relative to 1996 are about 7% in 1998 and about
10% in 2003. The lifetime computed in the quiet region still decreases with solar activity, although the decrease is smaller.
On average, relative to 1996, the lifetime decrease is about 4% in 1998, 10% in 2000, and 8% in 2003. Thus, measured lifetime
increases when regions of high magnetic activity are avoided. Moreover, the lifetime computed in quiet regions also shows
variations with the activity cycle. 相似文献
16.
We analyze multiple-wavelength observations of a two-ribbon flare exhibiting apparent expansion motion of the flare ribbons
in the lower atmosphere and rising motion of X-ray emission at the top of newly-formed flare loops. We evaluate magnetic reconnection
rate in terms of V
r
B
r by measuring the ribbon-expansion velocity (V
r) and the chromospheric magnetic field (B
r) swept by the ribbons. We also measure the velocity (V
t) of the apparent rising motion of the loop-top X-ray source, and estimate the mean magnetic field (B
t) at the top of newly-formed flare loops using the relation 〈V
t
B
t〉≈〈V
r
B
r〉, namely, conservation of reconnection flux along flare loops. For this flare, B
t is found to be 120 and 60 G, respectively, during two emission peaks five minutes apart in the impulsive phase. An estimate
of the magnetic field in flare loops is also achieved by analyzing the microwave and hard X-ray spectral observations, yielding
B=250 and 120 G at the two emission peaks, respectively. The measured B from the microwave spectrum is an appropriately-weighted value of magnetic field from the loop top to the loop leg. Therefore,
the two methods to evaluate coronal magnetic field in flaring loops produce fully-consistent results in this event. 相似文献
17.
L. K. Harra T. Magara H. Hara S. Tsuneta T. J. Okamoto A. J. Wallace 《Solar physics》2010,263(1-2):105-119
Active region magnetic flux that emerges to the photosphere from below will show complexity in the structure, with many small-scale fragmented features appearing in between the main bipole and then disappearing. Some fragments seen will be absorbed into the main polarities and others seem to cancel with opposite magnetic field. In this paper we investigate the response of the corona to the behaviour of these small fragments and whether energy through reconnection will be transported into the corona. In order to investigate this we analyse data from the Hinode space mission during flux emergence on 1?–?2 December 2006. At the initial stages of flux emergence several small-scale enhancements (of only a few pixels size) are seen in the coronal line widths and diffuse coronal emission exists. The magnetic flux emerges as a fragmented structure, and coronal loops appear above these structures or close to them. These loops are large-scale structures – most small-scale features predominantly stay within the chromosphere or at the edges of the flux emergence. The most distinctive feature in the Doppler velocity is a strong ring of coronal outflows around the edge of the emerging flux region on the eastern side which is either due to reconnection or compression of the structure. This feature lasts for many hours and is seen in many wavelengths. We discuss the implications of this feature in terms of the onset of persistent outflows from an active region that could contribute to the slow solar wind. 相似文献
18.
The `ribbons' of two-ribbon flares show complicated patterns reflecting the linkages of coronal magnetic field lines through
the lower solar atmosphere. We describe the morphology of the EUV ribbons of the July 14, 2000 flare, as seen in SOHO, TRACE,
and Yohkoh data, from this point of view. A successful co-alignment of the TRACE, SOHO/MDI and Yohkoh/HXT data has allowed us to locate the EUV ribbon positions on the underlying field to within ∼ 2′′, and thus to investigate
the relationship between the ribbons and the field, and also the sites of electron precipitation. We have also made a determination
of the longitudinal magnetic flux involved in the flare reconnection event, an important parameter in flare energetic considerations.
There are several respects in which the observations differ from what would be expected in the commonly-adopted models for
flares. Firstly, the flare ribbons differ in fine structure from the (line-of-sight) magnetic field patterns underlying them,
apparently propagating through regions of very weak and probably mixed polarity. Secondly, the ribbons split or bifurcate.
Thirdly, the amount of line-of-sight flux passed over by the ribbons in the negative and positive fields is not equal. Fourthly,
the strongest hard X-ray sources are observed to originate in stronger field regions. Based on a comparison between HXT and
EUV time-profiles we suggest that emission in the EUV ribbons is caused by electron bombardment of the lower atmosphere, supporting
the hypothesis that flare ribbons map out the chromospheric footpoints of magnetic field lines newly linked by reconnection.
We describe the interpretation of our observations within the standard model, and the implications for the distribution of
magnetic fields in this active region. 相似文献
19.
Magnetic reconnection in the temperature minimum region of the solar photosphere can account for the canceling magnetic features
on the Sun. Litvinenko (1999a) showed that a reconnection model explains the quiet-Sun features with the magnetic flux cancelation
rate of order 1017 Mx hr−1. In this paper the model is applied to cancelation in solar active regions, which is characterized by a much larger rate
of cancelation ∖ ge1019 Mx hr−1. In particular, the evolution of a photospheric canceling feature observed in an active region on July 2, 1994 is studied.
The theoretical predictions are demonstrated to be in reasonable agreement with the measured speed of approaching magnetic
fragments, the magnetic field in the fragments, and the flux cancelation rate, deduced from the combined Big Bear Hα time-lapse
images and videomagnetograms calibrated against the daily NSO/Kitt Peak magnetogram. Of particular interest is the prediction
that photospheric reconnection should lead to a significant upward mass flux and the formation of a solar filament. Hα observations
indeed showed a filament that had one of its ends spatially superposed with the canceling feature.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005284116353 相似文献
20.
We study the relationship between full-disk solar radiative flux at different wavelengths and average solar photospheric magnetic-flux
density, using daily measurements from the Kitt Peak magnetograph and other instruments extending over one or more solar cycles.
We use two different statistical methods to determine the underlying nature of these flux – flux relationships. First, we
use statistical correlation and regression analysis and show that the relationships are not monotonic for total solar irradiance
and for continuum radiation from the photosphere, but are approximately linear for chromospheric and coronal radiation. Second,
we use signal theory to examine the flux – flux relationships for a temporal component. We find that a well-defined temporal
component exists and accounts for some of the variance in the data. This temporal component arises because active regions
with high magnetic-field strength evolve, breaking up into small-scale magnetic elements with low field strength, and radiative
and magnetic fluxes are sensitive to different active-region components. We generate empirical models that relate radiative
flux to magnetic flux, allowing us to predict spectral-irradiance variations from observations of disk-averaged magnetic-flux
density. In most cases, the model reconstructions can account for 85 – 90% of the variability of the radiative flux from the
chromosphere and corona. Our results are important for understanding the relationship between magnetic and radiative measures
of solar and stellar variability. 相似文献
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